The Development of High-Tech Medical Diagnostic Tools

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The Development of High-Tech Medical Diagnostic Tools

Overview

Near the end of the twentieth century, high-tech diagnostic imaging techniques became powerful medical tools that allowed physicians to explore bodily structures and functions with a minimum of invasion to the patient. Advances in diagnostic technology allowed physicians the ability to evaluate processes and events as they occurred in vivo (in the living body). During the 1970s, advances in computer technologies allowed the development of accurate, accessible, and relatively inexpensive (when compared to surgical explorations) non-invasive technologies. Although relying on different physical principles (i.e., electromagnetism vs. sound waves), all of the high-tech methods relied on computers to construct visual images from a set of indirect measurements. The development of high-tech diagnostic tools was the direct result of the clinical application of developments in physics and mathematics. These technological advances allowed the creation of a number of tools that made diagnosis more accurate, less invasive, and more economical.

Background

The use of non-invasive imaging traces its roots to the tremendous advances in the understanding of electromagnetism during the nineteenth century. By 1900, physicist Wilhelm Konrad Roentgen's (1845-1923) discovery of high energy electromagnetic radiation in the form of x rays were used in medical diagnosis. Developments in radiology progressed throughout the first half of the twentieth century, finding extensive use in the treatment of soldiers during WWII.

Technological innovations in computing opened the door for the subsequent development and widespread use of sonic and magnetic resonance imaging (MRI). Better equipment and procedures also made diagnostic procedures more accurate, less invasive, and safer for patients. During the course of the twentieth century x-ray images that once took minutes of exposure could be formed in milliseconds with doses less than 1/50 of those used at the dawn of the century. Because of increased resolution that allowed physicians to see more clearly and with greater detail, physicians were increasingly able to make diagnosis of serious pathology (e.g., tumors) earlier. Earlier diagnosis often translates to a more favorable outcome for the patient.

During the early 1950s, the use of fluorescent screens allowed physicians their first real-time look into the body. Used in connection with improved contrast mediums (dyes that allow physicians to see vessels and internal organs), real-time diagnosis became a way for physicians to see the dynamics of disease.

Although nuclear medicine traces its clinical origins to the 1930s, the invention of the scintillation camera by American engineer Hal Anger in the 1950s brought nuclear medical imaging to the forefront of diagnostics. Nuclear studies involve the introduction of low-level radioactive chemicals that are consequently transported throughout the body to target organs and tissues. The scintillation camera measured and created images from the gamma rays emitted from these radioactive chemicals, enabling physicians to detect tumors or other disease processes. The basic techniques of the scintillation, or Anger camera, are the most widely used tools in nuclear medicine today, and gave rise to modern imaging systems such as the P.E.T. (positron emission tomography) scanner.

The development of noninvasive diagnostic techniques allowed physicians the opportunity to probe the body with safety and precision. Medical imaging encompasses a number of subspecialties, including x ray, computed tomography, magnetic resonance imaging, ultra-sound, scanning, and endoscopy. In conjunction with the injection of various dyes and markers, these techniques allow physicians to view the dynamic workings of the body (e.g., the flow of blood through arteries and veins).

The development of powerful, high-tech diagnostic tools in the latter half of the twentieth century was initially the result of fundamental advances in the study of the reactions that take place in excited atomic nuclei. Applications of what were termed nuclear spectroscopic principles became directly linked to the development of non-invasive diagnostic tools used by physicians.

In particular, Nuclear Magnetic Resonance (NMR) was one such form of nuclear spectroscopy that eventually found widespread use in the clinical laboratory and medical imaging. NMR is based on the observation that a proton in a magnetic field has two quantized spin states. Accordingly, NMR distinguishes between different types of organic molecules and, although there are complications due to interactions between atoms, in simple terms, NMR allowed physicians to see pictures representing the larger structures of molecules and compounds (i.e., bones, tissues, and organs) obtained as a result of measuring differences between the expected and actual numbers of photons absorbed by a target tissue.

Groups of nuclei brought into resonance, that is, nuclei absorbing and emitting photons of similar electromagnetic radiation (e.g., radio waves), make subtle yet distinguishable changes when the resonance is forced to change by altering the energy of impacting photons. The speed and extent of the resonance changes permit a non-destructive determination of anatomical structures. This form of NMR is used by physicians as the physical and chemical basis of a powerful diagnostic technique termed Magnetic Resonance Imaging (MRI).

Magnetic Resonance (MR) technologies relied on advances in physics during the 1950s. The development of MR imaging, attributed to English scientist Paul Lauterbur, was used in clinical trials during 1980. By the mid-1980s MR imaging was an accepted and widely used diagnostic technique.

MRI scanners rely on the principles of atomic nuclear-spin resonance. Using strong magnetic fields and radio waves, MRI collect and correlate deflections caused by atoms into images of amazing detail. The resolution of MRI scanner is so high that they can be used to observe the individual plaques in multiple sclerosis.

Impact

Late in the twentieth century, diagnostic tools moved into the operating room. So called "image-guided surgical methods" have allowed surgeons to more accurately determine the locations of tumors, lesions, and a host of vascular abnormalities. A corollary benefit of these techniques allows surgeons to track the positions of surgical instruments. Rapidly advancing computer technology and imaging, when used in conjunction with optical, electromagnetic, or ultrasound sensors, allow physicians to make real-time diagnosis a part of surgical procedures.

Principals of SONAR technology (originally developed for military use) found clinical diagnostic application with the development of ultrasound during the 1960s. A sonic production device termed a transducer was placed against the skin of a patient to produce high frequency sound waves that were able to penetrate the skin and reflect off internal target structures. Modern ultrasound techniques using monitors allow physicians real-time diagnostic capabilities. By the 1980s, ultrasound examinations became commonplace in the examination of fetal development.

The advent of other imaging techniques allowed for less potentially damaging forms of diagnosis. Ultrasonic Doppler techniques are used to identify pathology related to blood flow (e.g., arteriosclerosis). Specialized types of scanning using Doppler techniques are also used to identify heart valve defects.

Microscopes using ultrasound can be used to study cell structures without subjecting them to lethal staining procedures that can also impede diagnosis. Ultrasonic microscopes differentiate structures based on underlying differences in pathology. Ultrasonics are also the least expensive of the latest high-tech innovations in diagnostic imaging.

Mammography, or x-ray visualization of the breast, became a common diagnostic procedure in the 1960s, when physicians demonstrated its usefulness in the diagnosis of breast cancer. Initially, mammograms were used to aid in diagnosis only, and the x-ray dose to the tissue was relatively high. In 1973, the Breast Cancer Detection Demonstration Project, a five-year study of over 250,000 women, helped to establish mammography as an effective screening tool for breast cancer detection. Today, modern mammography machines allow greater precision of breast tissue imaging with less radiation exposure to the patient. Mammography is a standard recommended screening procedure, and is credited with reducing breast cancer mortality in women over 50.

During the early 1970s, enhanced digital capabilities spurred the development of Computed Tomography (derived from the Greek Tomos meaning slice) imaging, also called CT, Computed Axial Tomography, or CAT scans, invented by English physician Godfrey Hounsfield. CT scans use advanced computerbased mathematical algorithms to combine different reading or views of a patient into a coherent picture usable for diagnosis. Hounsfield's innovative use of high-energy electromagnetic beams, a sensitive detector mounted on a rotating frame, and digital computing to create detailed images earned him the Nobel Prize. As with x rays, CT scan technology progressed to allow the use of less energetic beams and vastly decreased exposure times. CT scans increased the scope and safety of imaging procedures, allowing physicians to view the arrangement and functioning of the body's internal structures on a small scale.

American chemist Peter Alfred Wolf's (1923-1998) work with positron emission tomography (PET) led to the clinical diagnostic use of the PET scan, allowing physicians to measure cell activity in organs. PET scans use rings of detectors that surround the patient to track the movements and concentrations of radioactive tracers. The detectors measure gamma radiation produced when positrons emitted by tracers are annihilated during collisions with electrons. PET scans have attracted the interest of psychiatrists for their potential to study the underlying metabolic changes associated with mental diseases such as schizophrenia and depression. During the 1990s PET scans found clinical use in the diagnosis and characterizations of certain cancers and heart disease, as well as clinical studies of the brain.

MRI and PET scans, both examples of functional imaging, are the subject of increased research and clinical application. They are used to measure reactions of the brain when challenged with sensory input (e.g., hearing, sight, smell), activities associated with processing information (e.g., learning functions), physiological reactions to addiction, metabolic processes associated with osteoporosis and atherosclerosis, and to shed light on pathological conditions such as Parkinson and Alzheimer's disease.

During the 1990s, the explosive development of information technologies and the Internet allowed physicians to make diagnosis from remote locations and to tele-conference over real-time data. Multiple imaging is becoming an increasingly important tool to physicians. These and other high-tech innovations may one day contribute to the speed and accuracy of diagnosis, minimizing the need for invasive surgeries, and allowing exquisite precision when surgery is necessary.

BRENDA WILMOTH LERNER